Manx Shearwater

Characterized as a medium-sized procellariid, this marine species is highly adapted for a life spent almost entirely over the open ocean. It measures between 12 to 15 inches (30 to 38 cm) in length, boasts a wingspan spanning 30 to 35 inches (76 to 89 cm), and weighs approximately 350 to 575 grams. The plumage displays a stark, highly diagnostic contrast between a sooty-black upperpart and a pure white underpart, with a sharp boundary running just below the eye. Its long, narrow, and stiff wings are structurally perfected for dynamic soaring close to the sea surface. The bill is slender, dark gray to blackish, featuring prominent tubular nostrils at its base and a sharp hook at the tip designed for gripping slippery prey. Its legs, colored pinkish on the inner side and bluish-black on the outer side, are set far back on its body, making terrestrial locomotion awkward while greatly optimizing underwater swimming efficiency.

Geographical distribution This long-distance migrant breeds predominantly in the North Atlantic, with the vast majority of the global breeding population concentrated on offshore islands around Great Britain and Ireland, alongside smaller but significant colonies in Iceland, the Azores, Madeira, the Canary Islands, and localized spots off eastern Canadá. Following the breeding season, it undertakes an extraordinary transequatorial migration of over 6,000 miles (10,000 km) to winter in the highly productive waters of the South Atlantic Ocean, specifically off the continental shelves of Brazil, Uruguay, and northern Argentina, exhibiting an exceptional level of philopatry by returning to the exact same nesting sites year after year.

Habitat: It is an exceptionally pelagic bird that occupies open oceanic waters, particularly over continental shelves and upwelling zones where marine nutrients are highly concentrated. Outside of the nesting period, it remains entirely at sea, coping with diverse marine climates ranging from cool subpolar waters to warmer subtropical zones during migration. It requires terrestrial environments solely for reproduction, choosing remote predator-free offshore islands, coastal cliffs, steep grassy slopes, and boulder fields with friable soil that allow for excavation and provide shelter from aerial and terrestrial threats.

Feeding Operating as a specialized marine carnivore, its diet consists primarily of small shoaling pelagic fish, such as sand eels, herrings, sprats, anchovies, and sardines. It also opportunistically consumes squid, small crustaceans, and organic discards from commercial fishing vessels. To capture food, it employs a combination of surface-seizing and plunge-diving, dropping from a few meters above the water and submerged swimming using its semi-folded wings for underwater propulsion. It can dive to depths of several meters to actively pursue fleeing schools of fish.

Behavior: The species is highly gregarious at sea, frequently gathering in immense groups known as "rafts" on the water´s surface near breeding colonies during the late afternoon. On land, it exhibits strictly nocturnal habits, arriving and departing from nesting sites only under the cover of complete darkness to mitigate the risk of predation by large gulls and skuas. Because of its rear-mounted legs, it is incredibly clumsy on land, forced to awkwardly push itself forward on its belly. It has an incredibly precise navigation system based on olfactory cues, the Earth´s magnetic field, and celestial patterns. Their vocalizations at breeding colonies are extremely loud, eerie, and guttural, forming a chaotic chorus of cackles and screams coming from subterranean burrows.

Nesting This monogamous species establishes long-term pair bonds and demonstrates high site fidelity. The breeding cycle begins in spring, during which pairs excavate a deep underground tunnel up to 3 feet (1 meter) in length using their sharp claws and bills, or adapt existing rabbit burrows and rock crevices. The female lays a single white egg which is incubated by both parents in alternating shifts of several days, lasting for a total period of about 50 days. The chick is fed a highly concentrated stomach oil and semi-digested fish. After approximately 70 days, the parents abruptly abandon the chick, which remains in the burrow for a short fasting period before fledging alone at night to start its perilous migration to the southern oceans.

Conservation status It is currently evaluated as Least Concern (LC) on the IUCN Red List due to its immense global population and extensive distribution range. However, local populations face severe threats, most notably from introduced invasive predators (such as rats, feral cats, and American minks) that easily raid vulnerable subterranean nests. Additional anthropogenic threats include light pollution from coastal developments, which fatally disorients fledglings leaving their burrows, as well as marine plastic ingestion, commercial longline fisheries bycatch, and shifts in prey availability driven by global climate change.